Sealing device for bearing unit

ABSTRACT

A sealing device for a bearing unit, having a stationary part, which is in turn provided with a first metal screen, an elastomer coating co-moulded on to the first screen, and a radially inner contact lip belonging to the elastomer coating, and a rotatable part provided with a second metal screen with which the contact lip makes a sliding contact, the sealing device being provided with at least one appendage which faces a radially inner flanged ring of the bearing unit and interacts with this flanged ring to form a barrier against the entry of contaminants.

CROSS-REFERENCE RELATED APPLICATIONS

This application is based on and claims priority to Italian PatentApplication No. 102020000023791 filed on Oct. 9, 2020, under 35 U.S.C. §119, the disclosure of which is incorporated by reference herein.

TECHNICAL FIELD

The present application relates to a sealing device for a bearing unitand to the bearing unit provided with said sealing device. The sealingdevice and the bearing unit are preferably, but not exclusively, appliedto a wheel hub assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of various exemplary embodiments will hereinafter be describedin conjunction with the appended drawings, provided to illustrate andnot to limit the disclosed aspects, wherein like designations denotelike elements.

FIG. 1 is a cross section through a wheel hub assembly provided with abearing unit,

FIG. 2a is a detail of the wheel hub assembly of FIG. 1 in which thereis a sealing device for a bearing unit according to a first exemplaryembodiment in accordance with the present disclosure, housed between therings of the bearing unit,

FIG. 2b is a detail on an enlarged scale of a portion of the sealingdevice FIG. 2 a,

FIG. 3 is the same detail of the wheel hub assembly of FIG. 1, in whichthere is a sealing device for a bearing unit, in a second exemplaryembodiment in accordance with the present disclosure, housed between therings of the bearing unit, and

FIG. 4 is the same detail of the wheel hub assembly of FIG. 1, in whichthere is a sealing device for a bearing unit, in a third embodiment ofthe present application.

DETAILED DESCRIPTION

Exemplary embodiments may be applied to all generations of wheel hubassemblies. In particular, such applications comprise both the case inwhich the outer ring of the bearing unit is rotatable while the innerrings of the bearing unit are fixed and the opposite case in which theinner rings rotate and the outer ring is fixed. Upon reading thisdisclosure in full, one will appreciate that embodiments are alsosuitable for any type of rolling bodies (balls, rollers, taperedrollers, etc.).

Sealing devices may be two-part cassette seals, comprising a rotatableportion, mounted, for example, on the radially inner ring of the bearingunit, and a stationary portion, mounted, for example, on the radiallyouter ring of the bearing unit. Also by way of example, the stationaryportion comprises a metal screen interference-fitted on the radiallyouter ring, and an elastomer portion is co-moulded on to the metalscreen. A second, rotatable, metal screen is interference-fitted on tothe rotatable radially inner ring.

The stationary portion of elastomer material comprises one or more lipswhich contact the rotatable portion, and which provide a seal for theinside of the bearing unit.

Sealing means may consist of a single part, integral with one of therings of the bearing unit, in which at least one contact lip provides aseal by the interference with a surface of the other ring of the bearingunit which is created when the seal is assembled.

The typical design of a sealing device therefore comprises one or moreprojections, called lips, which, having different shapes andorientations (typically axial and radial), are in contact with rotatablesurfaces of the bearing unit: thus the sealing device prevents the entryof contaminants from the outside, protecting the internal components ofthe bearing unit, in other words the rolling bodies and the cagescontaining the rolling bodies themselves. Another important function ofa sealing device is that of preventing the outflow of lubricants presentinside the bearing unit.

A sliding friction force is created between these contact lips and thecorresponding rotatable contact surfaces of the bearing unit, resultingin a dissipation of energy. As a rule, the sealing capacity increaseswith the number of contact lips and their rigidity. However, when thereis an increase in these parameters there is also an increase in theamount of energy dissipation.

Furthermore, owing to the increase in global competition, customers ormotor manufacturers are constantly demanding ongoing technical andeconomical improvements in wheel hub assemblies. In particular, thedevelopment of technology is accompanied by a demand for components thathave low energy dissipation while also providing the same performance ascutting-edge solutions.

To overcome this technical problem, it would be ideal to have acontactless sealing device that would successfully prevent the entry ofcontaminants and the loss of lubricants without the dissipation ofenergy. A contactless sealing device does not operate correctly,especially in underwater environments.

A sealing device is provided having low energy dissipation but excellentsealing performance, which is free of the aforementioned drawbacks.

Purely by way of example and without limiting intent, exemplaryembodiments will now be described with reference to a bearing unit 30,preferably a wheel hub assembly for motor vehicles provided with abearing unit having a sealing device according to the presentapplication.

With reference to FIG. 1, a bearing unit or wheel hub assembly isindicated as a whole by 30.

The unit has a central axis of rotation X, and includes a rotatableradially inner flanged ring 20, a stationary radially outer ring 31, afurther rotatable radially inner ring 34 mounted on, and integral withthe flanged ring 20, a plurality of rolling bodies 32, 33, in thisexample balls, interposed between the radially outer ring 31 and theflanged ring 20, two cages 39 and 40 for keeping the rolling bodies ofthe rings of rolling bodies 32, 33 in position.

Throughout the present disclosure and claims, terms and expressionsindicating positions and orientations such as “radial” and “axial” areto be interpreted as relative to the central axis of rotation X of thebearing unit 30. On the other hand, expressions such as “axially outer”and “axially inner” relate to the assembled condition of the wheel hubassembly, and in the present case preferably relate to a wheel side andto a side opposite the wheel side, respectively.

The flanged ring 20 and the radially outer ring 31 define, betweenthemselves and at the opposed axial ends of the bearing unit 30, twospaces 35, 36 which, if not screened, would allow contaminants andimpurities to enter the bearing unit 30.

Therefore, in order to screen the bearing unit 30, at least one sealingdevice, e.g., 50, 60, 70, made in accordance with the presentdisclosure, is mounted inside at least one of the two spaces 35, 36.

Normally, the sealing devices 50 comprise two metal screens facing eachother, at least one of which is provided with one or more sealing lipsof elastomeric material in sliding contact with the other screen, or asingle metal screen carrying one or more sealing lips of elastomericmaterial which slidingly contact a sliding surface of the bearing unit30 in relative motion with respect to the seals themselves.

In the following text, with reference to FIG. 2a , an illustration willbe given, according to an exemplary embodiment in accordance with thisdisclosure, of the case in which the sealing device 50 comprises arotating part provided with a metal screen 1, interference-fitted on tothe radially inner flanged ring 20, and a stationary part, which in turncomprises: a metal screen 10 interference-fitted on to a radially innersurface 31 a of the radially outer ring 31, an elastomer coating 2,co-moulded on the first screen 10, the development of which issubstantially radially internal and axially external with respect tosaid first screen 10, a radially inner contact lip 9, belonging to theelastomer coating 2 and therefore stationary, which makes a slidingcontact with the rotatable second screen 1.

According to exemplary embodiments, the sealing device 50 is providedwith an appendage 6 made of elastomer which faces the radially innerflanged ring 20 of the bearing unit 30 and acts as an external barrieragainst the entry of contaminants. In particular, according to thisfirst embodiment, the appendage 6 is part of the elastomer coating 2 andconstitutes the radially outer and axially inner portion thereof. Thewidth of the meatus G1 which is formed between the radially and axiallyouter end of the appendage 6 and the radially inner flanged ring 20 mayvary between 0 mm and 1.5 mm. In fact, since the appendage 6 is made ofelastomer, it would not be a problem (except for a small dissipation ofenergy due to friction) if the meatus G1 were eliminated; what isimportant is that its size should be kept as small as possible, andtherefore, given the tolerances on the components of the bearing unit,the maximum size is preferably limited to 1.5 mm. In order to eliminateeven the small dissipation, in some embodiments the meatus of G1 isnon-zero in length, e.g., at least about 0.1 mm.

Advantageously, the appendage 6 extends along an oblique direction lyingat an angle of between 0° and 35° to the axis of rotation X of thebearing unit 30, and has a thickness of between 0.5 mm and 1 mm.

Additionally, the minimum diameter D1 of the point of attachment R ofthe root of the appendage 6 to the elastomer coating 2 advantageouslyhas a minimum value of:

D 1 = Di + 3/4 * (De − Di)

where De and Di are, respectively, the radially outer and radially innerdiameters of the radially outer ring 31 radially outer of space 35 ofthe bearing unit 30.

Although not shown in the figure, the number of appendages 6 may also beequal to two. In this case, the second appendage will be in a radiallyouter position with respect to the first appendage 6, shown in FIG. 2.In particular, the second appendage will be positioned at a minimumradial distance of 2.5 mm from the first appendage 6.

With reference to FIG. 2b , the rotatable second metal screen 1 ispreferably shaped practically in the form of a “C”, with the radiallyouter limb 1′ inclined at an angle α of more than 1° to the axialdirection in the radially outward direction. An angle α is limited on anupper bound by ensuring that 1′ does not interfere with seal Gr or causelimb 1′ to interfere with elastomer coating 2 or lip 3 during operation.

Alternatively or additinoally, the rotatable second metal screen 1 isshaped practically in the form of a “C” and the distance d between theend of the radially outer limb 1′ and the elastomer coating 2 must begreater than 1 mm.

Advantageously, an elastomer coating 2 is provided with a radially innerlip 3 of small size, which does not make contact: the sealing device 50is therefore provided with a first radial labyrinth seal Gr formed bythe lip 3 that faces a radially outer limb of the metal screen 1.

Advantageously also, and with reference to FIG. 2b , the radially outerlimb 1′ of the screen 1 faces the elastomer coating 2 in an axialdirection, and a second, axial, labyrinth seal Ga is also formed, thisseal interacting with the radial labyrinth seal Gr to improve theefficiency of the barrier against external contaminants.

FIG. 3 shows another exemplary embodiment of the application, accordingto which a sealing device 60 comprises a rotating part provided with ametal screen 1, interference-fitted on to the radially inner flangedring 20, and a stationary part, which in turn includes a metal screen 10interference-fitted on to a radially inner surface 31 a of the radiallyouter ring 31, an elastomer coating 2, co-moulded around the firstscreen 10, and a radially inner contact lip 9, belonging to theelastomer coating 2 and therefore stationary, which makes a slidingcontact with the rotatable second screen 1.

According to one aspect, the sealing device 60 is provided with a metalappendage 7 which faces the radially inner flanged ring 20 of thebearing unit 30 and acts as an external barrier against the entry ofcontaminants. In particular, in like embodiments, an appendage 7 is partof the first screen 10 and constitutes the radially outer and axiallyouter portion thereof. The width of the meatus G2 which is formedbetween the radially and axially outer end of the appendage 7 and theradially inner flanged ring 20 may vary between 0.6 mm and 1.5 mm. Inthis solution, since the metal appendage 7 is made of metal, and giventhe constraint of keeping the size of a meatus G2 as small as possible(in this solution also, therefore, the maximum size is preferrably 1.5mm), it is impossible to specify a limit case in which the width of themeatus is zero: if two metal parts were to come into contact, theappendage 7 would act as a tool on the surface of the flanged ring 20,causing unacceptable erosive wear. A minimum value of 0.6, or about 0.6,for the width of the meatus G2 provides a safeguard against erosivewear. Evidently, since the appendage is made of metal and not elastomer,it is possible to specify a range of tolerances (0.6-1.5 mm) for themeatus G2 that is smaller than the range of tolerances for the meatus G1(0-1.5 mm).

Advantageously, the appendage 7 extends along an oblique direction lyingat an angle of between 30° and 89°, to the axis of rotation X of thebearing unit 30, and has a thickness of between 0.5 mm and 1 mm.

Additionally, the minimum diameter D1 of the point of attachment R ofthe root of the appendage 7 to the first screen 10 advantageously has aminimum value of:

D 1 = Di + 3/4 × (De − Di)

where De and Di are, respectively, the radially outer and radially innerdiameters of the radially outer ring 31 of the bearing unit 30.

Another exemplary embodiment is illustrated in FIG. 4. The aforesaidfigure shows a sealing device 70 which is similar overall to the sealingdevice 50 described and illustrated in FIG. 2. With respect to thesealing device 50, the sealing device 70 of FIG. 4 is provided with afurther axially outer elastomer coating 8 co-moulded on to the core ofthe second metal screen 1, which, as stated, is shaped practically inthe form of a “C”. This further elastomer coating 8 has the purpose ofcreating a further barrier to contaminants. The radially outer end ofthe elastomer coating 8 is formed to create a labyrinth L with thecylindrical portion 2′ of the elastomer coating 2. The labyrinth Lsubstantially reduces the entry of contaminants. This reduction isreinforced by the radial labyrinth Gr, formed by the lip 3 facing theradially outer limb of the second screen 1.

It should be noted that, although not shown in the figure, this furtherelastomer coating 8 may also be formed for the sealing device 60 shownin FIG. 3. In the latter case, the labyrinth will be formed by theradially outer end of the elastomer coating 8 with the cylindricalportion of the first screen 10. The barrier against contaminants createdby the further elastomer coating 8 is more effective because, when themetal appendage 7 is present, the size of the meatus G2 may be greaterthan that of the meatus G1 of the sealing devices 50, 70. In thislast-mentioned case also, the non-contacting lip 3 is not present.

It should be noted that the radially outer end of the rotatable furtherelastomer coating 8 does not, and must not, contact the stationaryelastomer coating 2. Otherwise a situation of relative sliding betweentwo elastomer components would arise, resulting in very high energydissipation due to friction. Conversely, if the further elastomercoating 8 defines the labyrinth L facing the first screen 10, therecould be contact between these two components, since one is made ofelastomer and the other of metal.

Additionally, the rotatable second screen 1 generates turbulence bycentrifugal action, which helps to drain the contaminant into thepre-chamber F, formed between the flanged ring 20, the outer appendage6, 7, and the further elastomer coating 8.

For the solution in FIG. 4, in the assembled condition the size of themeatus of the labyrinth L is between 0.1 mm and 1 mm: it should be notedthat the two elastomer coatings 2, 8 must never come into contact.

For the solution with the labyrinth formed between the further elastomercoating 8 and the first screen 10, the size of the meatus of thelabyrinth is between 0 mm and 1 mm in the assembled condition: in thiscase, the two components (the elastomer coatings 8 and the first screen)may come into contact.

Although not shown in FIGS. 2, 3, and 4, the sealing device 50, 60, 70could have a non-axially symmetrical geometry: in other words, itscomponents, including both the stationary and the rotatable parts, couldhave a circumferential development with a width of between 180° and260°. Thus, by accurately assembling the bearing unit and the wheel hubassembly so that the sealing device has the solid portion of itscomponents facing the top of the motor vehicle and is open towards thebottom of said motor vehicle, the sealing device is made to operate as abarrier against contaminant entering from the top of the motor vehicle,and allows these contaminants to flow out freely towards the bottom ofthe motor vehicle.

The insertion of the barrier or barriers, whether made of elastomer ormetal, enables the rate of flow of the contaminant into the sealingdevice to be reduced, and therefore makes it possible to design thinnercontact lips, thereby reducing the friction on the seal. At the sametime, for applications not requiring reduced friction, this solutionmakes it possible to improve the performance of a sealing device havingstandard contact lips.

Exemplary embodiments define a cassette sealing device having at leastone external barrier which faces a radially inner flanged ring of thebearing unit and has the function of better protecting the inside of thedevice and in particular the first operating dynamic sealing lip.

In fact, in order to obtain a significant reduction in friction, betterprotection is provided for the contact point of the sealing lip in orderto enable thinner lips to be designed.

The external barrier may advantageously be made of either elastomer ormetal. The external barrier is designed to reduce as far as possible therate of flow of the contaminant that can reach the sealing area of thecassette. The width of the meatus between the barrier and the radiallyinner flanged ring of the bearing unit must be as small as possible,while allowing for the tolerances of the components of the bearing unitand the bending stresses during the operation of the bearing unit.

In exemplary embodiments, the sealing device and its housing inside thebearing unit are made so as to increase the internal volumes, so thatthe latter can form larger reservoirs for the accumulation and drainageof contaminants that succeed in passing through the aforesaid externalbarrier.

The insertion of the barrier and the reduction of the rate of flow ofthe contaminant into the sealing device make it possible to designthinner contact lips, thereby reducing the friction on the seal. At thesame time, for applications not requiring reduced friction, thissolution makes it possible to improve the performance of a sealingdevice having standard contact lips.

Exemplary embodiments also relate to a bearing unit, and particularly toa bearing unit for a wheel hub assembly provided with a sealing deviceaccording to one of the embodiments of the present application.

Further preferred and/or particularly advantageous embodiments of theinvention are described according to the appended dependent claims.

In addition to the embodiments of the application as described above, itis to be understood that there are numerous other variants. It is alsoto be understood that these embodiments are provided solely by way ofexample and do not limit the object of the application or its possibleconfigurations. On the contrary, although the description given aboveenables a person skilled in the art to implement the present applicationaccording to at least one example of its embodiment, it is to beunderstood that numerous variations of the components described arepossible without departure from the object of the application as definedin the appended claims, which are interpreted literally and/or accordingto their legal equivalents.

1. A sealing device for a bearing unit comprising: a stationary partcomprising: a first metallic screen, an elastomer coating, co-moulded onthe first metallic screen, a contacting lip, wherein the contacting lipis radially internal of the first metallic screen, wherein the elastomercoating comprises the contacting lip; and a rotatable part provided witha second metallic screen on which the contacting lip makes a slidingcontact; wherein the stationary part further comprises at least oneappendage extending towards a flanged portion of the rotatable part andcooperate with the flanged portion to create a barrier against the entryof contaminants within the sealing device.
 2. The sealing device ofclaim 1, wherein the at least one appendage is made of an elastomer,wherein the at least one appendage is part of the elastomer coating, andwherein the at least one appendage comprises a radially outer andaxially outer portion of the elastomer coating.
 3. The sealing device ofclaim 2, wherein the width of a meatus (G1) which forms between theradially outer and axially outer end of the appendage and the flangedring is between 0 mm and 1.5 mm.
 4. The sealing device of claim 2,wherein the width of a meatus (G1) which forms between the radiallyouter and axially outer end of the appendage and the flanged ring isabout 0.1 mm.
 5. The sealing device of claim 2, wherein the at least oneappendage comprises two appendages radially spaced by at least 2.5 mm.6. The sealing device of claim 1, wherein the at least one appendage ismade of metal, wherein the at least one appendage is part of the firstmetallic screen and comprises the radially outer and axially outerportion of the first metallic screen.
 7. The sealing device of claim 6,wherein the width of a meatus (G2) which forms between the radiallyouter and axially outer end of the appendage and the flanged ringbetween 0.6 mm and 1.5 mm.
 8. The sealing device of claim 1, furthercomprising an additional elastomer coating co-moulded on the secondscreen.
 9. The sealing device of claim 8, wherein a radially outer endof the further elastomer coating extends radially towards a cylindricalportion of the elastomer coating defining a distance between 0.1 mm and1 mm.
 10. The sealing device of claim 8, wherein a radially external endof the further elastomer coating faces a cylindrical portion of thefirst screen at a distance between 0 mm and 1 mm.
 11. A bearing unitequipped with a sealing device of claim 1, housed in a cavity, thebearing unit further comprising: a flanged radially inner ring, whereinthe flanged radially inner ring is rotatable, a radially outer ring,wherein the radially outer ring is stationary an additional radiallyinner ring, rotatable, mounted on, and integral with the flangedradially inner ring, a plurality of rolling bodies interposed betweenthe radially outer ring and the radially inner rings.
 12. The sealingdevice of claim 1, further comprising a radially inner lip extendingfrom the elastomer coating in a direction radially inward and axiallytowards a flange extending radially from the stationary part defining ameatus (Gr) between an axially inner end of the radially inner lip and aradially outer limb of the second metal screen.